1. Field of the Invention
This invention relates generally to acoustic sensors, and, more particularly, to a apparatus for tensioning a piezoelectric film of an acoustic sensor.
2. Description of the Related Art
Acoustic or vibration sensors may be used in a variety of applications, such as automotive, medical, airline, oil and gas exploration, etc. These applications require that the sensors be able to detect vibrations that range from very high g-forces to very small or nano-vibrations. Sensors needed to detect nano-vibrations must be extremely sensitive, and, thus, are prone to miscalibration. That is, since the vibration being detected is so small, even a slight variation in the detected magnitude of the vibration can severely impact the accuracy of the response signal.
Some acoustic or vibration sensors have a sensing element suspended by a tensioned element so that they are free for limited movement when exposed to a vibration. Thus, when the sensor experiences vibrations, the sensing element moves by an amount, and at a frequency, directly proportional to the tension. Movement of the sensing element causes it to produce an electrical signal corresponding to the magnitude and frequency of the movement. Variations in the tension can severely impact the movement of the sensing element, and, thus, the electrical signals produced. That is, greater tension may reduce movement of the sensing element, and less tension may increase the movement of the sensing element.
If a plurality of the vibration sensors are disposed in an array, so that they are exposed to the same vibration, they should produce signals indicative of their position relative to the source of the vibration. That is, sensors closer to the vibration source should experience a larger vibration and produce a larger signal. However, if the tension varies among the sensors in the array, then sensors that are remote from the vibration source may produce a larger signal than sensors that are proximate the vibration source. Thus, variations in tension among vibration sensors in an array can greatly influence the accuracy of or invalidate information about the location, magnitude, and type of vibration experienced by the sensor array.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.